1. Field of the Invention
The invention pertains to the art of nuclear steam generator construction.
2. Description of the Prior Art
The general way in which new nuclear steam generators are made in the factory is to dispose a generally cylindrical generator shell in a horizontal position in the assembly area. The wrapper which is to be received horizontally into the shell has the general form of a rolled plate which is open along its longitudinal seam. The wrapper has a number of spacer elements strategically located on its outer circumference. This rolled wrapper with its spacers is inserted within the shell and is then expanded radially and welded along the longitudinal seam. Since the shell is not perfectly round, when the wrapper sheet is expanded it follows the non-round conformation of the shell with the result that the wrapper is also not perfectly round.
Tube support plates which are in the form of round discs provided with a large number of holes through which the generator tubes ultimately pass are then inserted into the wrapper plate and fixed at their periphery to the wrapper in generally uniform spacing from each other. The tube support plates are fabricated so that they have a substantially round periphery. However, since the wrapper in being expanded into the shell has been forced into an unround condition, the edges of the plates must be machined at various locations to fit the wrapper. This must also be accomplished with the holes in the series of tube support plates all being in axial alignment with each other from plate to plate.
This construction and the process involved required a relatively long time as well as extensive equipment and manpower, and is accordingly not suited for a field replacement of a wrapper within a nuclear containment building. Field retubing of nuclear steam generators is sometimes desirable when the number of tubes experiencing leaks in a given nuclear steam generator is so large that retubing or replacement of the steam generator must be effected.
Accordingly, it is the aim of the invention to provide a steam generator shell and wrapper construction and method of making the same which reduces the time, equipment and manpower requirements which are now associated with the factory shell and wrapper construction. The construction and method also must accommodate themselves to being carried out in part within a nuclear plant containment building.